CO_(2)-assisted oxidation dehydrogenation of light alkanes over metal-based heterogeneous catalysts

Light olefins are important platform feedstocks in the petrochemical industry,and the ongoing global economic development has driven sustained growth in demand for these compounds.The dehydrogenation of alkanes,derived from shale gas,serves as an alternative olefins production route.Concurrently,the target of realizing carbon neutrality promotes the comprehensive utilization of greenhouse gas.The integrated process of light alkanes dehydrogenation and carbon dioxide reduction(CO_(2)-ODH)can produce light olefins and realize resource utilization of CO_(2),which has gained wide popularity.With the introduction of CO_(2),coke deposition and metal reduction encountered in alkanes dehydrogenation reactions can be effectively suppressed.CO_(2)-assisted alkanes dehydrogenation can also reduce the risk of potential explosion hazard associated with O_(2)-oxidative dehydrogenation reactions.Recent investigations into various metal-based catalysts including mono-and bi-metallic alloys and oxides have displayed promising performances due to their unique properties.This paper provides the comprehensive review and critical analysis of advancements in the CO_(2)-assisted oxidative dehydrogenation of light alkanes(C2-C4)on metal-based catalysts developed in recent years.Moreover,it offers a comparative summary of the structural properties,catalytic activities,and reaction mechanisms over various active sites,providing valuable insights for the future design of dehydrogenation catalysts.

Zinc-modified Pt/SAPO-11 for improving the isomerization selectivity to dibranched alkanes

Zinc-modified Pt/SAPO-11 catalysts were prepared by incipient wetness impregnation and assessed in the hydroisomerization of n-octane.Their physicochemical properties were investigated using powder X-ray diffraction,scanning electron microscopy,nitrogen adsorption-desorption,pyridine-adsorbed infrared spectroscopy,temperature-programmed desorption of NH3,temperature-programmed reduction of hydrogen,temperature-programmed desorption of hydrogen,transmission electron microscopy,and X-ray photoelectron spectroscopy.The addition of zinc resulted in high dispersion of platinum.Zinc acted as a competitive adsorbent,changed the location of platinum.The catalyst with a zinc loading of 0.5%gave the highest selectivity to dimethylhexanes,but the conversion was lower than those achieved with the other catalysts.Dimethylhexanes have large molecular diameters,and therefore their diffusion may be difficult.This weakens the catalytic activity of the zinc-modified catalysts and lowers the n-octane conversion.

Ni-based catalysts derived from a metal-organic framework for selective oxidation of alkanes

Ni nanoparticles embedded in nitrogen-doped carbon（Ni@C-N） materials were prepared by ther-molysis of a Ni-containing metal-organic framework （Ni-MOF） under inert atmosphere. The as-synthesized Ni@C-N materials were characterized by powder X-ray diffraction, N_2 adsorp-tion-desorption analysis, scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, and X-ray photoelectron spectroscopy. The MOF-derived Ni-based mate-rials were then examined as heterogeneous catalysts for the oxidation of alkanes under mild reac-tion conditions. The Ni@C-N composites displayed high activity and selectivity toward the oxidation of a variety of saturated C–H bonds, affording the corresponding oxidation products in good-to-excellent yields. Furthermore, the catalysts could be recycled and reused for at least four times without any significant loss in activity and selectivity under the investigated conditions.

湛江湾柱状沉积物n-alkanes和PAHs组合分子特征及其环境指示作用

本文对湛江湾湾内、湾口和湾外柱状沉积物n-alkanes和PAHs的空间分布、成分谱特征和排放源进行调查分析。结果表明：（1）n-alkanes和PAHs的空间分布一致,浓度水平由高到低依次为：湾内、湾口、湾外,垂直变化不明显;（2）n-alkanes和PAHs的成分谱和L/H、CPI、Ant/（Ant＋Phe）、Flu/（Flu＋Pyr）、BaA/（BaA＋Chry）、IP/（IP＋BghiP）等特征参数比值以及主成分分析结果表明C25～C35高碳数n-alkanes的高等植物贡献具有绝对优势,C14～C24中低碳数的n-alkanes和PAHs则有共同的石油、化石燃料燃烧和生物质燃烧等人为源;（3）C14～C24中低碳n-alkanes与PAHs的源解析结果相同,其线性相关系数在0.67以上,表明两者具有较好的相关性,但两者之间的定量关系还需进一步的研究。本研究表明n-alkanes和PAHs对人为源的指示具有一致性,两者具有良好的相关性,能够较好地反映城市的社会经济状况,在进一步的研究中可以建立两者之间的定量关系并形成新的参数,提高人为源解析结果的准确性,深入反映人类活动对海洋环境的影响。

Constant Volume Spray Auto-ignition Study of Alkanes

Spray auto-ignition experiments were carried out in a constant volume combustion chamber for some pure alkanes(n-paraffins with different chain length, cyclohexane, n-butyl cyclohexane, and isooctane) and blends of n-decane with Standard Blended Fuel(isooctane/n-heptane) and product gasoline. Test results showed that the reaction activity of n-paraffins was relatively high. Meanwhile, the auto-ignition characteristics differed significantly with the molecular structures of alkanes. Adding different volume fractions of n-decane to Standard Blended Fuel and product gasoline could improve the fuel reaction activity at varying degree. Finally, functional groups effects were used to simulate the relationship between the molecular topology and the auto-ignition quality.

Predicting hydrate forming pressure of pure alkanes in the presence of inhibitors

An inherent problem with natural gas production or transmission is the formation of gas hydrates, which can lead to safety hazards for production/transportation systems, and substantial economic risks. Hydrate inhibition with different inhibitors such as, methanol, ethylene glycol （EG）, triethylene glycol （TEG）, and sodium chloride solution continues to play a critical role in many operations. An understanding of when the hydrates form in the presence of these hydrate inhibitors, is therefore necessary to overcome hydrate problems. Several thermodynamic models have been proposed for predicting the hydrate formation conditions in aqueous solutions containing methanol/glycols and electrolytes. However, available models have limitations that include the types of liquid, compositions of fluids, and inhibitors used. The aim of this study is to develop a simple-to-use correlation for accurate prediction of hydrate-forming pressures of pure alkanes in the presence of different hydrate inhibitors, where the obtained results illustrate good agreement with the reported experimental data.

Recent Results on Fast Flow Gas-Phase Partial Oxidation of Lower Alkanes

Recent experimental results and kinetic modeling of fast flow gas-phase oxidation of methane and other lower alkanes to methanol and other oxygenates are discussed, alongside with prospects and possible areas for applications of the processes.

Electrospinning synthesis of porous boron-doped silica nanofibers for oxidative dehydrogenation of light alkanes

The discovery of the high activity and selectivity of boron-based catalysts for oxidative dehydrogenation(ODH)of alkanes to olefins has attracted significant attention in the exploration of a new method for the synthesis of highly active and selective catalysts.Herein,we describe the synthesis of porous boron-doped silica nanofibers(PBSNs)100-150 nm in diameter by electrospinning and the study of their catalytic performance.The electrospinning synthesis of the catalyst ensures the uniform dispersion and stability of the boron species on the open silica fiber framework.The one-dimensional nanofibers with open pore structures not only prevented diffusion limitation but also guaranteed high catalytic activity at high weight hourly space velocity(WHSV)in the ODH of alkanes.Compared to other supported boron oxide catalysts,PBSN catalysts showed higher olefin selectivity and stability.The presence of Si-OH groups in silica-supported boron catalysts may cause low propylene selectivity during the ODH of propane.When the ODH conversion of ethane reached 44.3%,the selectivity and productivity of ethylene were 84%and 44.2%g_(cat)^(-1)s^(-1),respectively.In the case of propane ODH,the conversion,selectivity of olefins,and productivity of propylene are 19.2%,90%,and 76.6 jimol g_(cat)^(-1)s^(-1),respectively.No significant variations in the conversion and product selectivity occurred during 20 h of operation at a high WHSV of 84.6 h^(-1).Transient analysis and kinetic experiments indicated that the activation of O2 was influenced by alkanes during the ODH reaction.

SbCl_3 Catalyzed Solventless Synthesis of Bis(indolyl)alkanes under Grinding

A clean and efficient method for the synthesis of bis（indolyl）alkanes with antimony trichloride（SbCl3） as the catalyst under solvent-free grinding conditions is described. This method provides several advantages, such as simple work-up procedure, neutral conditions and high yields.

A viewpoint on catalytic origin of boron nitride in oxidative dehydrogenation of light alkanes

Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics,but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides.Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes,negligible formation of CO2,and remarkable catalyst stability.From this viewpoint,recent works on boron nitride in the oxidative dehydrogenations of ethane,propane,butane,and ethylbenzene are reviewed,and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions.After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence,we conclude that pure boron nitride is catalytically inert,and an activation period is required under the reaction conditions;this process is accompanied by an oxygen functionalization at the edge of boron nitride;the B-O species themselves have no catalytic activity in C-H cleavage,and the B-OH groups,with the assistance of molecular oxygen,play the key role in triggering the oxidative dehydrogenation of propane;the dissociative adsorption of molecular oxygen is involved in the reaction process;and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy.A new redox reaction cycle based on the B-OH sites is also proposed.Furthermore,as this is a novel catalytic system,there is an urgent need to develop new methods to optimize the catalytic performances,clarify the catalytic function of boron species in the alkane ODH reactions,and disclose the reaction mechanism under realistic reaction conditions.

Heterogeneous catalytic partial oxidation of lower alkanes(C_1–C_6) on mixed metal oxides

This review paper aims at analysing the state of the art for partial oxidation and oxidative dehydrogenation（ODH） reactions of lower alkanes C–Cinto olefins and oxygenated products（aldehydes, anhydrides,carboxylic acids） on metal oxide catalysts with cations of variable oxidation state, such as Mo and V in particular. Key parameters to be met by the catalysts, such as their redox properties, their structural aspects, active sites composed of ensembles of atoms isolated one from the others, mechanisms of reactions, are discussed. Main features of the different reactions of C–Calkanes and catalysts are analysed and their generalisation for determining more active and more selective catalysts is attempted. Prospective views for the future of the domain are proposed.

Enthalpies Estimation of Formation of Monosubstituted Alkanes by Interaction Potential Index

The interaction potential index IPI（X） of 16 Br, C1, I, NO2, CN, CHO, COOH, CH3, CH： kinds of substituents X （X---OH, SH, NH2, ：CH2, C-CH, Ph, COCH3, COOCH3） were proposed, which are derived from the experimental enthalpies of formation △fHФ （g） values of monosubstituted straight-chain alkanes. Based on the IPI（X） and polarizability effect index, a simple and effective model was constructed to estimate the △fHФ （g） values of monosubstituted alkanes RX （including the branched derivatives）. The present model takes into account not only the contributions of the alkyl R and the substituent X, but also the contribution of the interaction between R and X. Its stability and prediction ability was confirmed by the results of leave-one-out method. Compared with previous reported studies, the obtained equation can be used to estimate enthalpies of formation for much more kinds of monosubstituted alkanes with less parameters. Thus, it is recommended for the calculation of the △fHФ（g） for the RX.

A Quantitative Structure Property Relationship for Prediction of Flash Point of Alkanes Using Molecular Connectivity Indices

Many structure-property/activity studies use graph theoretical indices, which are based on the topological properties of a molecule viewed as a graph. Since topological indices can be derived directly from the molecular structure without any experimental effort, they provide a simple and straightforward method for property prediction. In this work the flash point of alkanes was modeled by a set of molecular connectivity indices （Х）, modified molecular connectivity indices （ ^mХ^v ） and valance molecular connectivity indices （ ^mХ^v ）, with ^mХ^v calculated using the hydrogen perturbation. A stepwise Multiple Linear Regression （MLR） method was used to select the best indices. The predicted flash points are in good agreement with the experimental data, with the average absolute deviation 4.3 K.

Even-carbon predominance of Monomethyl branched alkanes in Humic coal from Junggar Basin,NW China

A series of Monomethyl branched alkanes compounds were detected between nC14-nC36,in immature and low maturity Jurassic humic coal,Junggar basin.2-methyl alkanes and 3-methyl alkanes accounted for the vast majority of the compounds.It is worth noting that the2-methyl alkanes in the humic coal samples show an obvious distribution of even carbon predominances rarely reported in the literature.The results show that with the increase of Pr/Ph(pristane/phytane),the even carbon dominance of 2-methyl alkanes is more obvious,while the odd carbon number distribution of 3-methyl alkanes is weakened.As Pr/Ph increases in the humic coal,the relative content of the hopanes increased,while the relative content of 2-methyl alkanes and 3-methyl alkanes increases first and then decreases.

Use of the N-alkanes to Estimate Intake, Apparent Digestibility and Diet Composition in Sheep Grazing on Stipa brevifl ora Desert Steppe

The application of n-alkane as markers to estimate herbage intake, apparent digestibility and species composition of diet consumed by grazing sheep was studied. Six local Mongolian sheep were used to determine dry matter （DM） intake, apparent DM digestibility and species composition of diet during summer, autumn and winter. Animals were orally dosed twice daily with n-alkane gelatin capsules containing 60 mg C32-alkane as an external marker. Diet composition was estimated by comparing the odd-chain n-alkanes pattern profile （C27-C31） of the consumed plant species with the n-alkanes fecal concentrations of grazing animals, using a non-negative least squares algorithm called EATWHAT software package. The alkane pair C32：C33 and C33 alkane were used to estimate DM intake and diet apparent DM digestibility, respectively. The results showed that daily dry matter intake of the sheep were 1.77, 1.61 and 1.18 kg d-1 in summer, autumn and winter, respectively. Apparent DM digestibility, crude protein （CP）, metabolizable energy （ME） and neutral detergent fiber （NDF） intake of diet consumed by sheep decreased significantly （P〈0.01） from summer to winter, with no evident changes in ADF and ADL intake. Diet composition indicated Artemisia frigida Willd was the most dominant diet component, contributed 79.68, 68.12 and 86.26% of sheep＇s diets in summer, autumn and winter, respectively. Cleistogenes songorica Ohwi and Convolvulus arnmannii Desr were the important components of the diet. Although Stipa breviflora Griseb is one of the main plant species in the study area, the sheep rarely choosed it. The study indicated that CP and ME in diet consumed by sheep were deficient in winter. Therefore, appropriate supplementation strategies should be indispensable during this period.

Supercooling Suppression of Microencapsulated n-Alkanes by Introducing an Organic Gelator

Supercooling of the microencapsulated phase change materials（PCMs） during cooling usually happens. This phenomenon can interfere with heat transfer and is necessary to further overcome. In this study, mela- mine-formaldehyde microcapsules containing two n-alkane PCMs, namely, n-dodecane（Cl2） or n-tetradecane（C14） were prepared by in situ polymerization. A small amount of n-hexatriacontane（C36） was introduced as an organic ge- lator into the core of microcapsules to cope with the supercooling problem. Analyses demonstrate that supercooling of the microencapsulated C12 or C14 was significantly suppressed by adding 3%（mass fraction） C36, without changing the spherical morphology and dispersibility. It could be also found that the enthalpy of microencapsulated CI2 or C14 containing C36 was similar to that of microencapsulated n-alkanes without C36, whereas the difference between onsets of crystallization and melting（degree of supercooling） is similar to that of those of pure n-alkanes, suggesting the re- markable suppression ability of the organic gelator on supercooling.

Acyclic Alkanes in the Soil over Heshang Cave in Qingjiang, Hubei Province

The reports that relate to the biomarker＇s fate and characteristics of the modern soil in the karst area are very lacking. By using gas chromatography-mass spectrometry （GC-MS）, a series of biomarkers were identified from the soils collected over Heshang cave （和尚洞） in Qingjiang （清江）, Hubei （湖北） Province. The distribution of n-alkanes is mainly from C2s to C33 in carbon number, with a maximum at C31. They have a strong odd-over-even carbon number predominance. These characteristics represent an input mainly from higher plants. The lipid parameters, including CPIh （carbon preference index）, Rb/t（ratio of lower- to higher-molecular-weight homologues） and ACL （average chain length）, show comparable trends with depth, probably reflecting vegetation change and microbial degradation. Series of monomethylalkanes and diploptene are present in the extractable organic matter; they might be derived from soil microbes, cyanobacteria in particular.

Particulate n-alkanes and fatty acids in the Changjiang river system

Particulate samples were collected from the Changjiang river system during a flood period, in May 1997, and POC, stable isotope and lipids associated with particles were examined. Results showed the decrease （0.84% ～ 1.88%） of organic carbon content from the upper reaches to the estuary.δ^13 values of particulate organic carbon was in the range of -24.9×10^-3 to -26.6×10^-3, which were close to the isotopic signature of continental C3 vegetation. Total particulate n-alkanes concentrations varied from 1.4 to 10.1μg/dm^3,or from 23.7 to 107μg/g of total suspended matter. Fatty acids were present in all the samples, from 1.4 to 5.4μg/dm^3, with saturated and unsaturated straight-chain and branched compounds in the carbon number range from C12 to C30. Both δ^13 and the ratio of carbon content to nitrogen content indicate the predominance of terrestrial inputs （soil organic matter） among the particles. The biomarker approach has been used to identify the relative portion of terrigenous and autochthonous fraction in the particulate samples. The distribution of fatty acids suggests a striking phytoplanktonic and microbial signal in most particle samples. The terrestrial alkanes are used to estimate the contribution of terrestrial inputs along the mainstream.

Composition index of n-alkanes and paleoenvironmental study in sediments of the Arctic

This paper reports different concentration patterns of n-alkanes distribution in the sedi- ments from the Chukchi Sea, the Bering Sea in the Arctic. Factor statistical analysis method is used for studying the source of n-alkanes and paleoenvironment. The result shows that n-alkanes is in the range of nC15-nC33 and n-alkane distribution patterns are characterized by two modes. The first mode belongs to the higher molecular with MH being nC25-nC27, CPI > 1 and with remarkable odd-even dominance. They are of terrigenous plant origin. The second one belongs to lower carbon range with MH being nC17 -nC20, CPI > 1 and with indistinct odd-even dominance. Therefore they are contributed by marine bio- logicla inputs. The contribution of land origin is larger than that of marine source. Pr/Ph is lower than 1 in the investigated area, which indicates the depositional environment of reducing reaction with lower oxygen. The result of factor analysis has good agreement with composition characteristics of n-alkanes in the sediment.

Paleoenvironmental implications of Holocene long-chain n-alkanes on the northern Bering Sea Slope

The records of high-resolution terrestrial biological markers （biomarkers） from Core B2-9 from the northern Bering Sea Slope over the last 9.6 ka BP were presented in the study. Variations in input of terrestrial long-chain n-alkanes （referred to as n-alkanes） and vegetation structure in their source regions were investigated. The results show that the nCz7 is the main carbon peak and has the greatest contribution rate of the total n-alkane content; this might be related to the abundance of woody plants and their spatial distribution in the source region, nC23 is another n-alkane having a relatively high content; this was mainly derived from submerged plants widespread along the coastal areas in the northern hemisphere. Total n-alkane content dropped quickly at ca. 7.8 ka BP, ca. 6.7 ka BP and ca. 5.4 ka BP, and was followed by four relatively stable stages mostly controlled by sea-level rise, climate change and vegetation distribution in the source region. Variation in carbon preference index （CPI） indicates that the n-alkanes primarily originated from higher land plants, and the average chain length （ACL） and nCa1/nC27 ratio reveal the relatively stable presence of woody/herbaceous plants during the Holocene, and dominate woody plants in most of the time. Simultaneous variation in total n-alkane content, nC27 content and its contribution, CPI, ACL and nC31/nC27 ratio over several short periods suggest that the growth rate of the woody plant n-alkane contribution was lower than that of herbaceous plants and fossil n-alkanes under the particular climatic conditions of the source region.